Methods of transposing sheet materials

ABSTRACT

METHODS OF RADIALLY TRANSPOSING RADIALLY ADJACENT ELECTRICALLY CONDUCTIVE SHEET MATERIALS IN AN ELECTRICAL WINDING, WHICH INCLUDE FORMING NOTCHES IN OPPOSITE EDGES OF THE THROUGH THE NOTCH IN THE OTHER. THE NOTCHES ARE FORMED BY CUTTING EACH OF FIRST AND SECOND SHEET MATERIALS TO BE TRANSPOSED INTO FIRST AND SECOND SHEET MATERIALS TO BE TRANSCUT ENDS OF THE PORTIONS IN A PREDETERMINED MANNER. THE FIRST AND SECOND PORTIONS IN A PREDETERMINED MANNER. THE FIRST ARE ELECTRICALLY JOINED, WITH THE FOLDING PROVIDING A NOTCH IN ONE EDGE OF THE RESULTING COMPOSITE CONDUCTOR, AND THE SECOND AND FIRST PORTIONS OF THE FIRST AND SHEET MATERIALS ARE ELECTRICALLY JOINED, WITH THE FOLDING PROVIDING A NOTCH IN THE OPPOSITE EDGE OF THIS COMPOSITE CONDUCTOR. THE COMPOSITE CONDUCTORS ARE INHERENTLY RADIALY TRANSPOSED BY THE METHOD OF FORMING THEM, AND THE TRANSPOSED CONDUCTORS MAINTAIN RADIAL ALIGNMENT BY EACH PROCEEDING THROUGH THE NOTCH IN THE OTHER.

United States Patent [72] Inventors Frank W. Benke 394,212 1/1925 Germany 174/34 Sharon, Pm; Prima ry ExammerJohn F. Campbell 2] A I N gg g Assistant ExaminerCarl E. Hall 22} Firlagd. 0. Jub s 1968 Attorneys-A. T. Stratton, Donald R. Lackey and F. E.

451 Patented June 28,1971 [73] Assignee Westinghouse Electric Corporation,

Pittsburgh, Pa.

ABSTRACT: Methods of radially transposing radially ad- [54] METHODS OF TRANSPOSING SHEET MATERIALS jacent electrically conductive sheet materials in an electrical 14 Claims, 43 Drawing Figs. winding, which include forming notches in opposite edges of 52 us. Cl 29/624 hmugh in The "mches'are fmmed by 29/605 156/49 174/34 6/ 336/!87 cutting each of first and second sheet materials to be trans- [51] Int. Cl 1101i 7/06 posed into first and Second separate portions and folding the 501 Field or Search 29/605 ends P'mmmincd The first 624 156/49. 174/34 1 336/187. 310/213 and second portions of the first and second sheet materials are electrically joined, with the folding providing a notch in one [56] References Cit d edge of the resulting composite conductor, and the second UNITED STATES PATENTS and first portions of the first and second sheet materials are electrically joined, with the folding providing a notch in the 3 gg z f' 3 opposite edge of this composite conductor. The composite 338235 5/1968 Migni t 336 187x conductors are inherently radially transposed by the method c l of forming them, and the transposed conductors maintain FOREIGN PATENTS radial alignment by each proceeding through the notch in the 129,788 7/1919 Great Britain 310/213 other.

(ZZQ 240 /22 {I98 1 r L 196 228 23Q 9 PATENTEUJUNZS [an 3.587169 sum 3 [1F 5 208 m FIG.!2.

METHODS OF TRANSPOSING SHEET MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to methods of transposing electrically conductive sheet materials in windings for electrical inductive apparatus, such as transformers and reactors, and more particularly to methods of transposing sheet conductors in such windings.

2. Description of the Prior Art Constructing windings for electrical transformers of metallic foil, sheet or strip material, has certain advantages over windings constructed of wire-type conductor. For example, windings constructed of wire or strap conductor require electrical insulation between radial layers of conductors, as well as turn-to-turn insulation, which increases the size of the winding. Further, with wire or strap wound windings, it is difficult to accurately determine the electrical center of the winding, i.e., the axial location which divides the ampere turns equally, especially when the winding is tapped. When the primary and secondary windings of the transformer are assembled in concentric adjacentrelation, any axial displacement of their electrical centers creates a force during short circuit stresses which forces the windings axially apart.

Electrical windings constructed of sheet material, such as copper or aluminum strip or foil, wherein the winding includes a plurality of superposed conductor turns, requires only turnto-turn insulation, as the conductor turns extend across the axial dimension of the coil; or where axially aligned, electrically connected part-coils are used, the conductor of each part-coil would'extend across the axial dimension of its associated part-coil. Since the turn-to-turn voltages are relatively low, the turn-to-tum insulation may be a thin strip of insulating material, such as kraft paper, which is wound between the conductor turns at the time the winding is constructed, or it may be a thin coating of an insulating enamel applied to one or both of the major surfaces of the sheet material. Thus, the space factor of an electrical winding formed of' electrically conductive sheet materials is excellent, resulting in a smaller winding, which reduces the size of the magnetic core and the casing, and thus reduces the size, weight and cost of the transformer, Also, since the electrical center of a winding constructed of sheet material is the same as its mechanical center, there will be less force tending to separate concentric windings axially during short circuit stresses The sheet winding is also inherently stronger than a winding formed of wire or strap conductor, as the individual conductors of a wire-type winding may be deformed by short circuit stresses, eventually causing tum-to-turn and layer-to-layer short circuits, while the sheet conductor turns resist deformation, and are not as subject to movement and vibration which may abrade and wear the insulation disposed between two conductors.

When the current rating of an electrical winding is increased, more conductor cross-sectional area is required to carry the increased current, if the winding temperature is to be maintained below the maximum temperature allowable for the class of insulation used. However, since eddy current losses are proportional to the square of the dimension of the conductor at right angles to the leakage flux, it is common to subdivide the required-conductor area into two or moreparallel connected conductive elements, which are electrically insulated from one another, except at their common connections at the start and finish of the winding, and at any tap connections to the winding. The stranding of the conductor is easy to accomplish with wire, strap, or sheet-type conductive material. With wire or strap conductors, the required plurality of strands are electrically insulated from one another, and then may be taped together to form a single structure which facilitates winding. With sheet, the required number of sheet conductors are wound simultaneously, in superposed relation, with electrical insulating means disposed between the conductors.

Subdividing the conductive cross-sectional area required into a plurality of parallel connected elements, however, introduces loses due to circulating currents in the parallel connected elements. Losses due to circulating currents may be reduced by transposing the relative radial positions of the conductive elements, in an effort to subject each element to the same net leakage flux and, therefore, equalize: the induced voltages in the various elements and provide a net induced voltage around each loop of substantially zero. When using wire or strap conductor, the transposing of the individual strands, is relatively easy, with a number of transposing arrangements being known in the art for transposing any SUMMARY OF THE INVENTION Briefly, the present invention discloses new and improved methods for radially transposing electrically conductive sheet materials. One of the disclosed methods of radially transposing first and second electrically conductive cutting both the first and second sheet materials into first and' second portions, folding the cut ends of the first and second portions of each of the sheet materials in a predetermined manner, electrically joining the cut and folded ends of the first and secondportions of the first andsecond sheet materials, respectively, toform a first composite conductor in which the folds define a notch in a predetermined edge thereof, and joining the cut and folded ends of the second and first portions of the first and second sheet materials, respectively, to form a second composite conductor in which the folds define a notch in a predetennined edge thereof. This method of joining transposes the relative radial positions of the first and second composite sheet conductors, with each composite sheet conductor passing through the notch in the other in order to allow the transposition to be made while keeping the conductors in radial alignment.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. I is a perspective view of an electrical winding formed of first and second electrically conductive sheet materials, which may utilize the teachings of the invention to transpose the radial positions of the sheet materials;

FIGS. 2A through 2D are schematic diagrams of typical transposing arrangements which may utilize the methods of the invention;

FIGS. 3A and 3B illustrate the steps in a method, according to the teachings of the invention, for providing a notch in the edge of an electrically conductive sheet material;

FIGS. 4A and 4B illustrate the method shown in FIGS. 3A and 3B, for providing a notch in the opposite edge of an electn'cally conductive sheet material;

FIG. 5 illustrates the transposition of the sheet conductors shown in FIGS. 38 and 48;

FIG. 6 illustrates a sheet of electrical insulating material, which may be used to electrically insulate the two transposed sheet conductors shown in FIG. 5;

FIG. 7 illustrates the sheet materials which formed transposition of FIG. 5, electrically insulated from one another with the sheet of insulating material shown in FIG. 6;

FIGS. 8, 9 and I diagrammatically illustrate the steps of another method of transposing electrically conductive sheet materials, according to the teachings of the invention;

FIGS. 11A through 11F illustrate the steps of a method for preparing notches in sheet conductors for use with the transposition shown in FIGS. 8,9 and FIG. 12 illustrates a transposition performed with the prepared sheet conductors shown in FIGS. [IE and HF;

FIGS. 13A and 13B illustrate sheets of electrical insulating material which may be used to insulate the transposition shown in FIG. 12;

FIG. 14 illustrates the transposition of FIG. 12, insulated with the sheet materials shown in FIGS. 13A and 13B;

FIGS.15A through ISJ illustrate the steps of another method of preparing notches in electrically conductive sheet material, for use with the transposition shown in FIGS. 8, 9 and 10;

FIG. 16 illustrates a transposition performed with the prepared sheet material shown in FIGS. E and 15F;

FIGS. 17A through 17F illustrate the steps of another method of preparing notches in sheet material for use with the transposition shown in FIGS. 8, 9 and 10; and

FIG. 18 illustrates a transposition performed with the prepared sheet materials shown in FIGS. 17E and 17F.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, and FIG. 1 in particular, there is shown an electrical winding 10 of the type which may utilize the teachings of the invention. While winding 10 is shown as being rectangular, it may be round, or any other desired shape. Electrical winding 10, which may be a primary or a secondary winding for an electrical transformer, or a coil for a reactor or autotransformer, is constructed of at least two sheets 12 and 14 of electrically conductive sheet material, such as copper or aluminum. Sheets 12 and 14 may be strip or foil of any desired thickness T and width W, as required by the specific application. Typical thickness dimensions are in the range of 0.008 inch to 0.063 inch, and typical width dimensions are in the range of 10 inches to 56 inches, for electrical power transformers, but it will be understood that the invention will apply to the transposition of sheet conductors having any desired dimensions. For example, distribution-type transformers may utilize sheet conductors having smaller thicknesses and with dimensions.

As the thickness dimension T of the sheet material increases, itbecomes more difficult to wind the sheet material about a mandrel with a good space factor. Further, as the thickness dimension T increases, the losses due to eddy currents increase, Therefore, for both mechanical and electrical reasons, when the current requirements dictate a thickness dimension which exceeds, in general, 0.063 inch for power transformers, the required conductor cross-sectional area may be subdivided into a plurality of sheet conductors which are wound simultaneously and connected in parallel at the ends of the winding.

As shown in FIG. 1, sheet conductors 12 and 14 are connected to a power terminal 16, such as by welding, and the two sheet conductors are wound about a common axis 18, forming a plurality of superposed or nested conductor turns 20. The sheets of electrically conductive material may be wound directly upon an expandable mandrel, or they may be wound about a winding tube 22, which is disposed on a mandrel.

In order to prevent the two sheet materials from contacting one another, except at the ends of the winding, and at any tap connection points, and from contacting the conductors of adjacent turns the two sheet materials must be electrically insulated. The electrical insulation between conductor turns, and between the multiple conductors of each turn, may be an insulating coating disposed on one or both of the major opposed surfaces of the sheet materials, such as an enamel coating formed of an epoxy, or other good electrical insulating material; or, the electrical insulating may be one or more sheets or strips of insulating material, such as kraft paper, which are disposed between the electrically conductive sheet materials, and adjacent the outer surface of at least one of the sheets, and wound simultaneously therewith.

After winding 10 is complete, the two sheet materials 12 and 14 will have their ends connected to another power lead, similar to the lead 16.

While dividing the conductive cross-sectional area required into a plurality of parallel connected conductive elements reduces the eddy current losses of the electrical winding, the reduction in losses may be offset by an increase in losses due to circulating currents in the parallel connected elements. Losses due to circulating currents in the parallel connected elements. Losses due to circulating currents may be reduced by transposing the relative radial positions of the parallel con nected elements, in an attempt to subject all of the parallel connected elements to the same net leakage flux. With two parallel connected elements, such as shown in FIG. 1, a standard transposition wherein the radial sequence of the conductors is reversed, will produce a perfect transposition, if performed at the midpoint of the total conductor length, since each conductor occupies the relative radial position of the other for substantially the same conductor length. The standard transposition is shown schematically in FIG. 2A, wherein two conductors A and B are connected in parallel between terminals 25 and 27, and transposed at transposition point 24 to reverse their radial positions.

The sheet conductors l2 and 14, as shown in FIG. I, start at terminal 16 with sheet conductor 12 being the inner conductor, and their relative radial positions are transposed or reversed at transposition 26, such that sheet conductor 14 becomes the inner conductor. As will be hereinafter described, the standard transposition 26 may be performed according to the teachings of this invention.

FIG. 2B is a schematic diagram illustrating how three sheet conductors A, B and C, connected in parallel, between terminals 28 and 30, may be transposed, using all standard transpositions, to provide a perfect transposition wherein each Sheet conductor successively occupies the positions of the other sheet conductors, for substantially the same distance. The standard transposition alternates between the two outer conductors and the two inner conductors, until completing five transpositions. Thus, the two inner conductors B and C are transposed at point 32, the two outer conductors A and C are transposed at point 34, the two inner conductors A and B are transposed at point 36, the two outer conductors B and C are transposed at point 38, and the two inner'conductors C and A are transposed at point 40.

In addition to making the standard transposition with two conductors, any number of conductors may-be divided into two groups and the two groups transposed with a standard transposition. This type of transposition is shown schematically in FIGS. 2C, with conductors A, B, C and D being connected between terminals 42 and 44 and transposed at transposition 46. Transposition 46, however, since it does not reverse the positions of the conductors, is technically not a standard transposition, and is often called a complete transposition. Also, it is not a perfect transposition, as the conductors do not occupy the positions of all of the other conductors.

Four conductors may be perfectly transposed using a combination of standard and complete transpositions. This arrangement is shown schematically in FIG. 2D, with conductors A, B, C and D being connected in parallel between terminals 47 and 48. The first transposition point includes a complete transposition 50, the next point includes two standard transpositions 52 and 54, and the next transposition point includes a complete transposition 56. This arrangement causes each conductor to occupy each of the radial positions for the same distance. This result can also be achieved by using two standard transpositions at the first transposition point, a complete transposition at the next transposition point, and two standard transpositions at the last transposition point.

The different transposing arrangements shown in FIGS. 2A, 2B, 2C and 20 are examples of interleaving arrangements which may be used with electrically conductive sheet materials, according to the teachings of the invention. Other arrangements, however, may also be used.

Copending application Ser. No. 742,722, filed July 5, 1968, which is assigned to the same assignee as the present application discloses transposing arrangements for sheet-type electrically conductive materials wherein a notch is disposed in opposite edges of the superposed conductors to be transposed, with each conductor proceeding to its transposed position through the v notch in the other conductor. Also disclosed in this copending application are methods of forming a notch in electrically conductive sheet material, which relate to forming the notch while minifying the amount of scrap, minifying current crowding in the vicinity of the notch, and preventing the current density in the narrowed portion of the sheet from increasing substantially above that in the unnarrowed portion. The present application relates to new and improved methods of forminga notch in electrically conductive sheet materials, and also to new and improved methods of transposing sheet materials which do not require the relative positions of the rolls of supply material be changed after each transposition point.

FIGS. 3A, 3B, 4A,4B, 5,6 and 7 illustrate the steps of a new method of forming notches in electrically conductive sheet material, which is essentially scrapless, and which maintains substantially the same current density in the portion of the sheet material adjacent the notch, as that in the unnarrowed portion. FIGS. 3A and 3B illustrate the steps of a method of forming a notch or opening, on one edge of an electrically conductive sheet material, with FIG. 3A illustrating a sheet 60 of electrically conductive material, such as copper or aluminum, having first and second edges 62 and 64, respectively, and first and second ends 66 and 68, respectively. End 66 may be form a partially wound electrical coil or winding, such as from winding 10 shown in FIG. I, which is wound to the point where transposition 26 is to be performed. End 68 is attached to a roll of supply material, disposed on a suitable payoff reel (not shown).

The first step is to cut the sheet 60 with first and second cuts 70 and 72, respectively, starting from the edge in which the notch is tobe provided, In this instance, the sheet 60 is cut from the second edge 64. The cuts 70 and 72 are cut at predetermined angles 74 and 76 with respect to the edge, with the cuts converging towards one another, until reaching predetermined points with respect to the width of the sheet 60. They should proceed at least to the centerline 78 of the sheet width and preferably a short distance beyond, in order to simplify the electrical insulating of the transposition. The two cuts are spaced from one another such that they meet the predetermined point relative to the width of the strip a predetermined distance apart. The predetermined angles 74 and 76 shown in FIG, 3A are 30, as this has beenfound to provide excellent results. The exact angle, however, is not critical. If the angles 74 and 76 are too great, the transition zone between the unnarrowed width and the narrowed width of the sheet will be too short, causing undue current crowding, which in turn increases the temperature of the conductor in this area. If the angles 74 and 76 are too small, the notch and therefore the resulting transposition will become large with respect to the diameter of the conductor turns at the transposition point, which should be avoided. The angle of 30 has been found to be suitable, since the current density in the narrowed portion will be substantially the same as in the unnarrowed portion of the sheet, when following the teachings of the disclosed method.

The next step, shown in FIG. 3B, is to fold the section between cuts 70 and 72 along fold line 80, back against the portion of the sheet which is disposed between the ends of the cuts 70 and 72 and the edge 62, with the folding of this section automatically forming a notch or opening 82 in edge 64. If the cuts have extended past centerline 78, the outer edge of the folded section will extend past edge 62 by a predetermined small amount, and this small excess may be trimmed to coincide with edge 62, if desired. The amount trimmed, however, is negligible compared with its affect on the current density, and it is the only scrap in this method.

The next step, also shown in FIG. 3B, is to electrically join the cut edges of the folded section to the immediately adjacent portion of the sheet conductive material, as shown at 84 and 86. The electrical joining may be accomplished by welding, soldering, brazing, or any other suitable method. The portion of the sheet material between the apex of the notch 82 and edge 62 is thus a double section, doubling the cross-sectional area of the conductive material in this area, which maintains the current density through the narrowed section of the sheet at substantially the same magnitude as it is in the remaining portions of the sheet. If the folded sections were not electrically joined to the main portion of the sheet, the result would be the same as if the folded sections were removed from the sheets, which would then double the current density adjacent the notch and substantially increase the temperature of the strip in this area. V

FIGS. 4A and 4B illustrate the method steps of FIGS. 3A and 3B, for providing a notch in the other edge of sheet conductive material. Specifically, FIG. 4A illustrates a sheet of electrically conductive materialhaving first and second edges 92 and 94, respectively, and first and second ends 96 and 98. End 96 may be from a partially wound electrical coil, and end 98 may be connected to a roll 'of supply material. Sheet material 90 is also provided with first and second cuts 100 and 102 which are disposed at angles 104 and 106 with edge 92. The angles I04 and 106 should be the same as angles 74 and 76 shown in FIG. 3A, andthe cuts 100 and. 102 should proceed to the same point relative to the strip width that the cuts 70 and 72 proceeded to in FIG. 3A, Thus, the cuts 100 and 102 should proceed just beyond the centerline 108 of the strip or sheet conductor 90, with the section of conductor between the two cuts being folded along fold line 110, as shown in FIG. 4B. The cut edges of the folded section are then electrically joined to theimmediately adjacent sheet material, as shown at 114 and 116. The folding of the sheet material between the cuts automatically forms an opening or notch 112 in the edge 92 of the sheet material.

FIG. 5 illustrates a transposition formed with the prepared sheet conductors 60 and 90 shown in FIGS. 3B and 48, with sheet 60 proceeding to its new position through the notch 112 in sheet material 90, and sheet material 90 proceeding to its new position through the notch 82 in the sheet conductive material 60. i

Since sheet conductors 60 and 90 have the edges of their folded sections electrically joined to the immediately adjacent surface of the sheet conductor, the plurality of parallel connected sheet conductors may be best insulated with a separate sheet of electrical insulating material, instead of an insulating coating applied to the sheet materials, which would have to be removed, at least in the area of the joint, for most types of joining methods. Thus, the electrical winding would have a sheet of insulating material disposed between each adjacent pair of sheet conductors, which would be wound simultaneously with the winding of the sheet conductors. The sheet insulating material which separates the two sheet conductors to be transposed, may be prepared as shown in FIG. 6, at the point which is to be adjacent the transposition of the sheet conductors. FIG. 6 illustrates a sheet 124 of insulating material having first and second edges 126 and 128, and having cuts 130 and 132 which start at edges 126 and 128, respectively. Cuts 130 and 132 may be made along lines which are perpendicular to the edges I26 and 128, or they may be cut at an angle thereto, such as at the same angle which the notch makes with the edge of the sheet conductive material. Cut 130 should proceed towards edge I28 at least for the dimension necessary to receive the portion of sheet material 60 between edge 62 and fold line 80 on sheet material 60, and cut I32 should proceed towards edge 126, at least for the dimension necessary to receive the portion of sheet material 90 between edge 94 and fold line 110.

FIG. 7 illustrates the transposition 120 shown in FIG. 5, with sheet insulating material 124 shown in FIG. 6 disposed between sheet conductors 60 and 90, on both sides of the transposition point. Sheet conductive material 60 proceeds through the opening provided by cut 130 in the sheet of insulating material 124, and sheet conductive material 90 proceeds through the opening provided by cut 132.

The method of forming the transposition 120 shown in FIG. provides a transposition having negligible scrap, without requiring that any of the conductors be turned over as they proceed through the transposition point, with completely severing a conductor, and without substantially increasing the current density through the narrow portion of the conductor adjacent the notch. However, transposition 120 does require that the positions of the two reels of conductive material which supply sheet conductors 60 and 90, have their relative positions reversed after the transposition point. This could be accomplished by exchanging the positions of the supply rolls on the payoff reels, or by moving the payoff reels and their associated supply rolls. While this change in the relative positions of the supply rolls may be readily accomplished if the payoff reels are designed for this specific function, it would also be desirable to be able to perform essentially scrapless transpositions of sheet conductors, without changing the relative positions of the supply rolls, or payoff reels, after each transposition point.

FIGS. 8, 9 and 10 diagrammatically illustrate a transposing arrangement for sheet conductors which does not require that the positions of the conductor supply rolls be interchanged after each transposition point. FIG. 8 illustrates a mandrel 140 having two electrically conductive sheet materials 144 and 146 being simultaneously would thereon, from supply rolls 148 and 150, respectively. When the point in the winding build is reached where a radial transposition of the sheet conductors is required, each of the sheet conductors144 and 146 is severed, as shown in FIG. 9, and their cut ends prepared, such as by folding, such that the cut end of conductor 146 from the supply roll 150 may be electrically and mechanically joined to the cut end of conductor 144 from winding 142, and automatically form a notch in the desired edge of the resulting composite conductor; and, the cut end of conductor 144 from supply roll 148 may be electrically and mechanically joined to the cutend of conductor 146 from winding 142, and automatically form a notch in the opposite edge of the resulting composite conductor. The forming of the composite conductors transposes the sheet conductors without requiring that the relative positions of the supply rolls be changed, with transposition point 152 illustrating that the inner conductor on the winding 142 is now connected to supply roll 150, becoming the outer conductor after the transposition point 152, and illustrating that the outer conductor 146 on winding 142 is now connected to supply roll 148, becoming the inner conductor after the transposition point 152. Thus, the radial transposition of the two sheet conductors has been accomplished, without requiring that the positions of the conductor supply reels be interchanged. Each composite sheet conductor proceeds through the notch in the other, in order to complete the transposition while maintaining radial alignment of the conductors.

FIGS. 11A through 11F illustrate the steps of a first method for providing notches in sheet conductors, for completing the transposition shown in FIGS. 8, 9 and 10, with the method shown in FIGS. 11A through 11F being completely scrapless, and performing the transposition without any substantial increase in the current density adjacent the notches in the sheet materials.

FIG. 11A illustrates a sheet 160 of electrically conductive material which is superposed with sheet 162 of electrically conductive sheet material shown in FIG. 11C, which sheet materials are to have their relative radial positions transposed. Sheet material 160 shown at 11A has first and second edges 164 and 166, and first and second ends 168 and 170. End 168 is from a partially finished electrical winding, and end 170 is from a supply roll of sheet material.-

Electrically conductive sheet material 162, shown in FIG. 11C, has first and second edges 172 and 174 and first and second ends 176 and 178. End 176 is from the unfinished winding, and end 178 is connected to a roll of supply material.

Each of the sheet materials 160 and 162 are cut into first and second portions, with sheet material 160 being cut along line 180 into first and second portions 192 and 194, and with sheet material 162 being cut along line 182 into first and second portions 196 and 198. Line 180 on sheet material 160 is disposed at a predetermined angle 200 with respect to edge 164, such as 30. The angle selected determines the angle of the converging portions of the hereinafter formed notch, and is thus selected according to the same considerations hereinbefore set forth relative to the selection of the angles for the cuts in FIGS. 3A and 4A. Line 182 on sheet conductor 162 is a mirror image of line 180, with the slope of lines 180 and 182 being of like magnitude, but of opposite sign.

After the step of cutting each of the sheet materials 160 and 162 into first and second portions along their respective cut lines 180 and 182, each of the resulting portions have cut ends which have a triangular point thereon. Each of the triangular points are folded back along bend or fold lines which are perpendicular to the side or edge of the sheet which intersects the triangular point, with the fold line intersecting the diagonally cut edge. The exact point at which the fold line intersects the cut edge is determined by the desired depth of the notch. Since the notch must extend to at least the midpoint of the strip width, and preferably slightly beyond in order to facilitate insulating the transposition, the fold lines should have a dimension slightly less than one-half of the width dimension of the sheet. Thus, in sheet material 160, as shown in FIG. 11A, the triangular point of portion 192 has a fold line 184 disposed perpendicular to edge 164, which intersects the diagonal cut line 180 short of the centerline 171, and portion 194 of electrically conductive sheet material 160 has a bend line 186 which is disposed perpendicular to edge 166, and which intersects the diagonal out line 180 short of centerline 171.

In like manner, portions 196 and 198 of sheet material 162 have bend lines 190 and 188, respectively, similarity disposed on their respective triangular points, with respect to the sheet centerline 173.

FIGS. 11B and 11D illustrate portions 192 and 194 of sheet 160, and portions 196 and 198 of sheet 162, respectively, with their triangular points folded back along their respective bend lines. The next step, also illustrated in FIGS. 11B and 11D, is to electrically join the diagonally cut edge of each of the folded sections to the surface of the immediately adjacent portion of the sheet material, in order to increase the cross-sectional area of the sheet conductor adjacent the narrow portion of the sheet. Thus, as shown in FIG. 118, the diagonally cut edge 204 of the folded section on portion 192 is electrically joined to the surface of portion 192, such as by welding, and the diagonally cut edge 206 of the folded section on portion 194 is electrically joined to the surface of portion 194.

In like manner, the diagonally cut edges 208 and 210 of the folded sections on portions 196 and 198, respectively, are joinedto the immediately adjacent portion of its respective sheet material.

The next steps, shown in FIGS. 115 and 11F, are to join the folded ends of the first and second portions 192 and 198 of sheet conductors 160 and 162, respectively, and to join the folded ends' of the second and first portions 194 and 196 of sheet materials 160 and 162, respectively. Thus, as shown in FIG. 11E, portion 192 is joined to portion 198 along line 226, such as by welding, soldering, brazing or any other suitable joining means, which provides a first composite sheet conductor 220 having a notch 222 disposed on one edge thereof. As illustrated in FIG. 11F, portion 196 is joined to portion 194, along line 228, which provides a second composite sheet conductor 230 having a notch 224 disposed on the side opposite the side of sheet 220 in which notch 222 is disposed.

The composite sheet conductors 220 and 230 automatically transpose the relative radial positions of the two sheet conductors which form the winding, which is inherent in the way the composite conductors are formed. FIG. 12 illustrates the resulting transposition 240, in which composite sheet conductor 220 is directed through the notch 224 in composite sheet conductor 230, and composite sheet conductor 230 is directed through the notch 222 in composite sheet conductor 220, in order to keep the transposed sheets radially aligned. Assuming portion 192 was the outer conductor on the electrical winding being formed, and portion 196 was the inner conduct or, the outermost supply reel would have been connected to portion 192, and the innermost supply reel would have been connected to portion 196. Now, after transposition 240, the outermost supply reel is connected to the inner conductor at joint 228, and the innermost supply reel is connected to the outer conductor at joint 226. Thus, the winding, up to the transposition 240, includes inner and outer sheet conductors, which are transposed to become the outer and inner sheet conductors, respectively, after the transposition. Further, this radial transposition of sheet conductors has been achieved without scrap, and without requiring the rolls of supply material to be moved relative to one another. The narrowed portion of each composite sheet conductor has two thicknesses of sheet material, thus enabling the current in the conductors to flow through the transposition point without a substantial increase in the current density.

The transposition 240 shown in FIG. 12 may be electrically insulated with a sheet of insulating material similar to the sheet insulator 124 shown in FIG. 6, which would be assembled with the transposition as shown in FIG. 7. Instead of twice cutting the sheet insulator which separates the two transposed conductors, it would be suitable to modify two of the sheets of insulating material which are adjacent the transposed sheet materials, which requires that each be out only once, but requires the relative positions of supply rolls of insulation to be changed. Thus, as shown in FIGS. 13A and 138, sheet insulating materials 250'and 260 may be provided, respectively, with sheet insulating material 250 having first and second edges 252 and 254, and a centerline 258, and with sheet insulating material 260 having first and second edges 262 and 264, and a centerline 258. Each of the sheet insulating materials 250 and 260 have a single cut, which may be made at any desired angle with either side, as long as the cut reaches to at least the midpoint of the sheet. As shown in FIG. 13A, sheet insulating material 250 may have a cut 256 which extends diagonally from edge 252 to substantially the sheet centerline 258, and as shown in FIG. 138, sheet insulating material 260 may have a cut 266 which extends diagonally from edge 264 to substantially the sheet centerline 268. The angles and slopes of cuts 256 and 266 are shown to be similar to the angles and slopes of the adjacent edges of the notches in the sheet conductors. Thus, each sheet of insulating material is superposed over one of the sheet conductors as they approach the transposition point. Each sheet of insulating material may then be out along one of the edges of the notch of its adjacent sheet conductor, and the sheet conductor and its immediately superposed sheet insulating material may progress through the transposition point together, by changing the relative positions of the supply rolls of insulating material. FIG. 14 illustrates the transposition 240 shown in FIG. 12, insulated with the sheet insulating materials 250 and 260, shown in FIGS. 13A and 138.

Another method of insulating the two transposed conductors from one another would be to simply cut the sheet of insulating material, which separates the two conductors completely in two, at the midpoint of the transposition, and then start the sheet of insulating material between the two conductors as they proceed away from the transposition.

FIGS. 15A through 15F illustrate another method of providing notches for transposing sheet conductors according to the teachings of the invention shown in FIGS. 8, 9 and 10. The hereinbefore mentioned copending application teaches how to mark a sheet conductor with three bend lines, and to fold the conductor along the bend lines to provide a notch on one edge of the sheet, without scrap, without cutting the sheet, and without substantially increasing the current density adjacent the notch. The plurality of folds adjacent the notch increase the effective cross-sectional area of the conductive material, allowing the current to flow through the narrowed area at substantially the same current density as in the unnarrowed area. This method of the copending application produces excellent results electrically, but the method of achieving the transposition of the conductors requires that each sheet conductor be turned over as it proceeds through the transposition point, and the relative positions of the supply rolls must be changed after each transposition point. By following the teachings of this invention, the same three bend lines may be utilized to build up the cross-sectional area of the'conductive material adjacent the notch, and the sheet material may be transposed without turning the sheet material over, and without changing the relative positions of the supply rolls.

More specifically, FIG. 15A illustrates a sheet 280 of electrically conductive sheet material having first and second edges 282 and 284, respectively, and first and second ends 286 and 288, respectively. End 286 may be from a partially completed electrical coil winding, and end 288 may be connected to a roll of supply material. In this embodiment of the invention, the riotch is to proceed to the centerline of the sheet material. Therefore, following the teachings of the hereinbefore mentioned copending application, the three bend lines are marked on the sheet, with the first bend line 290 being perpendicular to the edges of the sheet, and the second and third bend lines 292 and 294 extending outwardly from opposite ends of the first bend line 290, intersecting the opposite edge at 45 angle. When the notch is to proceed to the centerline of the strip width, the second and third bend lines intersect the edges of the sheet material a dimension, from where the first bend line intersects that edge of the sheet material, which is equal to the length of the first bend lines. Since the first bend line, in this instance, is equal to the width of the sheet material, the angles of the second and third bend lines 292 and 294 are 45 with respect to the edges of the sheet.

The next step, as shown in FIG. 15A, is to lay out the pattern inwhich the sheet material 280 is to be cut, in order to form first and second portions 298 and 300. The first step in laying out the cut pattern is to draw a line 304 between bend lines 2 92.and 294, which line proceeds along the centerline 296 of the sheet conductor. Then, the intersection of cut line 304 with bend line 292 is used to start a line 302 which is perpendicular to edge 284. The intersection of out line 304 with bend line 294 is used as the starting point in which to draw line 306 perpendicular to edge 282. The lines 302, 304 and 306 form the pattern in which sheet material 280 is to be cut into the two portions. I

FIG. 15C illustrates a sheet 310 of electrically conductive material, which is superposed with sheet material 280 shown in FIG. 15A, and is to be radially transposed therewith. Sheet material 310 includes first and second edges 312 and 314, respectively, and first and second ends 316 and 318. End 316 may be connected to the partially would electrical winding, and end 318 may be connected to a second roll of supply material. Three bend lines 320, 322 and 324 are marked on the sheet material 310, with the bend lines being placed such that they are a mirror image of the bend lines 290, 292 and 294 shown in FIG. 15A. in other words, bend line 320 is placed similar to bend line 290, perpendicular to edges 312 and 314, but the second and third bend lines 322 and 324 start from opposite ends of the first bend line compared with the first and second bend lines 292 and 294 shown in FIG. ISA. The pattern on which material 310 is cut, is also a mirror image of the pattern on which sheet conductor 298 shown in FIG. 15A is cut. The first step is similar to the first step of forming the cut pattern on conductor 280, with a line 334 being drawn along the centerline 326 of the sheet between bend line 322 and 324. The intersection of the cut lines 334 with the bend line 322 is sued as a point in which to draw a line 332 perpendicular to edge 312, and the intersection of cut line 334 with bend line 324 is used as the starting point for drawing the line 336 perpendicular to the edge 324 of the sheet material 310. The pattern on which sheet material 310 is to be cut, then follows the lines 332, 334, and 336.

After cutting sheet material 280 along lines 302, 304 and 306, which form two separate portions 298 and 300, portion 298 has its cut end folded along the portions of the three bend lines thereon, and portion 300 has its cut end folded along the portions of the three bend lines which are disposed on it. The folds may be in any desired order, and they may be made towards the winding machine operator, away, or some may be made towards the operator and some away, as desired. FIG. B illustrates portions 298 and 300 after they have their cut ends folded, which provides four thicknesses of the sheet material at the edges 340 and 342 on portions 298 and 300, respectively. The edges 344 and 346 of the diagonally folded sections of portions 298 and 300, respectively, may be electrically joined to the immediately adjacent surface of sheet conductor, as illustrated, in order to utilize these folded sections as effective current carrying conductors. The edges of the folds defined by lines 348 and 350 and portions 298 and 300, need not be electrically joined to the immediately adjacent surface, as the current will flow through these portions of the sheet material without requiring an electrical connection at this point. However, edges 348 and 350 may be electrically joined to the immediately adjacent sheet material, if desired. If only three thicknesses of material are desired at edges 340 and 342, the diagonal folds which form edges 344 and 346 may be eliminated which, in addition to reducing the buildup at the edges 340 and 342, eliminates any brazing of the edges of the folds to the adjacent surface of the sheet. In this instance, the portion of bend line 292 from the intersection of cut lines 302 and 304, to its intersection with edge 284 would not be folded; and, the portion of bend line 294 from the intersection of cut lines 304 and 306, to its intersection with edge 282, would not be folded. In other words, the portion of bend line 412 which is on portion 420 would not be folded, and the portion of bend line 414 which is on portion 418, would not be folded. This embodiment is illustrated in FIG. 15G.

, In like manner, cutting sheet material 310 shown in FIG. 15C along the cut lines 332, 334 and 336, provides first and second sections 328 and 330. FIG. 15D illustrates portions 328 and 330 with their cut ends folded along the portions of the three bend lines which appear thereon, providing four thicknesses of sheet material along the lines 352 and 354. The edges 356 and 358 of the diagonal folds of portions 328 and 330, respectively, and the edges of the folded sections defined by lines 360 and 362, may or may not be electrically joined to the immediately adjacent sheet material, as desired. The folds which form edges 356 and 358 may be eliminated, as hereinbefore described relative to portions 298 and 300, which embodiment is shown in FIG. 15H.

The next step is to electrically join portion 328 of sheet material 310 with portion 300 of sheet material 280, by placing their edges 352 and 342 together, respectively, and welding, or otherwise suitably joining the portions along these adjacent surfaces. The electrical and mechanical connection of these two portions automatically provides a notch 366 in one edge thereof, and it provides a first composite conductor 370, as shown in FIG. 15E. If the alternative embodiment is followed therein the diagonal folds are eliminated, the first composite conductor would be as shown in FIGS. 15], and is given the reference numeral 370.

The next step is to electrically and mechanically join por tion 298 of sheet conductor 280 with portion 330 of sheet conductor 310, by placing their edges 340 and 354 together, and welding, or otherwise suitably joining the two portions along these edges. This step provides a composite conductor 380, as shown in FIG. 15F, having a notch 374 fonned in the edge which is opposite to the edge in which notch 366 is disposed in composite conductor 370. FIG. 15.] illustrates the Composite conductor formed when the two diagonal folds are eliminated, with the composite conductor of this embodiment being referenced 380.

The composite conductors 370 and 380 shown in FIGS. 155 and 15F automatically have their relative radial positions transposed as soon as they are formed, and as shown in FIG. 16, they form a transposition 382 in which composite conductor 370 is directed through the notch 374 in composite conductor 380, and composite conductor 380 is directed through the notch 366 in the composite conductor 370, in order to keep the transposed conductors radially aligned. Like the transposition 240 shown in FIG. 12, transposition 382, shown in FIG. 16 transposes the relative positions of two sheet conductors, without requiring that the rolls of supply material have their positions interchanged. The composite conductors 370' and 380' shown in FIGS. 151 and 15.! would be directed through the notch in the other, similar to that shown in FIG. 16 for composite conductors 370 and 380.

In most instances, it is not desirable for the notch in the sheet material to proceed only to the centerline of the sheet width, as it is more difficult to adequately electrically insulate the transposition when both of the notches meet at the centers of the sheets. FIGS. 17A through 17F illustrate how two sheets of electrically conductive material may be prepared, similar to the method shown in FIGS. 15A through 15F, except that the notches will proceed for a short dimension past the width of the strip, in order to separatethe notches from one another in the transposition. FIG. 17A illustrates a sheet 400 of electrically conductive material having first and second edges 402 and 404, respectively, and first and second ends 406 and 408. End 406 may be from a partially would electrical coil and end 408 may be connected to a roll of supply material. Three bend lines 410, 412 and 414 are marked on the sheet, with the first bend line 410 being disposed to form first and second angles 411 and 413 with edge 404, with the first angle 411 being less than and the second angle 413 being greater than 90; and, first and second angles 415 and 417 with edge 402, with the first angle 415 being greater than 90 and the second angle 417 being less than 90. The bend lines are then disposed within the angles which are less than 90, with the first bend lines 412 being disposed within angle 411, and with the second bend line 414 being disposed within the angle 417. Bend line 412 is disposed at that angle which will intersect edge 402 a dimension from the intersection of the first bend line 410 with edge 402 which is equal to the length of the first bend line 401. Bend line 414 is parallel with bend line 412, intersecting edge 404 a dimension from the intersection of the first bend line 410 with edge 404, which is equal to the length of the first bend line 410.

The pattern on which sheet material 400 to be cut is generated by drawing a first out line 424 through the midpoint of the sheet, represented by centerline 416, such that the dimension of the line 424 between the second and third bend lines 412 and 414 is equal to twice the distance desired between the apex of the notch in the sheet material and the edge of the sheet material nearest the apex. The intersections of the first cut line 424 with the second and third bend lines are then used as starting points from which to draw lines perpendicular to the adjacent edges of the sheet material. Thus, a line 422 is drawn from the intersection of cut line 424 with bend line 412, which is perpendicular to the edge 404, and a line 426 is drawn from the intersection of out line 424 with bend line 414, to the edge 402, with the line 426 being perpendicular to the edge 402. Sheet material 400 is cut along the lines 422, 424 and 426, to form first and second separate portions 418 and 420.

The sheet material to be radially transposed with sheet material 400 is sheet material 430 shown in FIG. 17C, which has first-and second edges 432 and 434, and first and second ends 436 and 438. The first end 436 is from the partially finished electrical winding, and the second end 438 is connected to a second roll of supply material. Sheet material 430 has three bend lines 440, 442 and 444 marked thereon, which are the mirror image of the bend lines 410, 412 and 414 shown in FIG. 17A. Sheet material 430, which has a centerline 446, has a cut pattern disposed thereon which is a mirror image of the cut pattern on sheet material 400 shown in FIG. 17A. Sheet material 430 has a cut pattern which includes lines 452, 454 and 456, with line 452 being perpendicular to edge 432 and line 456 being perpendicular to edge 434. The intersections of lines 452 and 456 with bend lines 442 and 444 are joined by line 454, which intersects the midpoint of the first bend line 440 at the centerline 446 of the sheet material. The lengths of lines 452, 454 and 456 are equal to the lengths of lines 422, 424 and 426, respectively, for sheet 400, and the respective angles formed by the cut and bend lines for sheets 400 and 430 are equal. Sheet material 430 is cut into first and second portions 448and 450, along a pattern defined by the lines 452, 454 and 456.

FIG. 17B illustrates the first and second portions 418 and 420 of the sheet material 400 shown in FIG. 17A, with its cut ends being folded along the portions of the bend lines disposed on their respective portions. Portion 418 has an edge 460 having four thicknesses of sheet material, and edges 464 and 468 of folded sections which may or may not be joined to its immediately adjacent sheet material, as desired. In like manner, portion 420 includes an edge 462 which has four thicknesses of conductive material, and edges 466 and 470 of folded portions which may or may not be electrically connected to the sheet material, as desired. The folds which form edges 464 and 466 may be eliminated, if desired, which will provide three thicknesses of material at edges 460 and 462, and which eliminates the brazing of any folded edges to the adjacent surface of the sheet, as hereinbefore described relative to FIGS. 15A-15J FIG. 17D illustrates the first and second portions 448 and 450 of the sheet material 430 shown in FIG. 17C, with its cut ends folded alongthe three bend lines. Portion 448 includes an edge 472 having four thicknesses of sheet material, and edges 476 and 480 of folded sheet material which may or may not be joined to the sheet conductor, as desired. Portion 450 includes an edge 474 having four thicknesses of conductive material, and edges 478 and 482 of folded sections which may or may not be joined to its immediately adjacent sheet material, as desired. The folds which form edges 476 and 478 may be eliminated, as hereinbefore described relative to portions 418 and 420.

The next step, as shown in FIG. 17E, is to join portion 448 to portion 420, by disposing edges 472 and 462 of portions 448 and 420 adjacent one another, and then electrically join them by welding, or any other suitable method. Joining portions 448 and 420 provides a composite sheet conductor 490 having a notch 494 in one edge thereof which proceeds beyond the centerline of the composite conductor.

The next step, shown in FIG. 17F, is to join portions 418 and 450 together, by disposing their edges 460 and 474 adjacent one another, and joining these edges by welding, or any other suitable means. As shown in FIG. 17F, joining portions 418 and 450 forms a composite conductor 500 having a notch 504 disposed in one edge thereof, with the apex of this notch extending beyond the centerline of the composite sheet material.

The composite conductors 490 and 500 shown in FIGS. 17B and 17F are radially transposed as soon as they are formed, forming a transposition 510 as shown in FIG. 18, in which the composite sheet conductor 490 proceeds through the notch 504 in composite. sheet conductor 500, and the composite sheet conductor 500 proceeds through the notch 494 in the composite sheet conductor 490, in order to keep the transposed conductors radially aligned. Since the apex of the notch 494 and the apex of the notch 504 proceed past the centerlines of their respective sheet materials, a clearance, given the reference numeral 512, will be provided between the notches,

which facilitates the insulating of the transposition. Transposition 510 may be insulated by using any of the hereinbefore mentioned arrangements, or any other suitable means.

In order to describe the steps of the various disclosed methods of transposing sheet conductors, it has been necessary to enumerate the steps in a certain order. It will be apparent that the order of performing certain of the steps may be changed, and these changes are within the scope of the invention.

In summary, there has been disclosed new an improved methods of forming transpositions of sheet conductive materials, and new and improved methods of forming notches in the edges of the sheet conductive materials, preparatory to the making of a transposition. The invention teaches a new transposing arrangement which is scrapless, which doesn't substantially increase the current density adjacent the notches in the sheet material, and which doesnt require that the relative positions of the supply rolls be changed after the transpositrons.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. A method of transposing superposed electrically conductive sheet materials, comprising the steps of:

providing first and second superposed sheet materials each having first and second edges, with their first edges being adjacent to one another, and their second edges adjacent to one another,

cutting the first sheet material into first and second portions each having a cut end and a second end,

cutting the second sheet material into first and second portions each having a cut end and a second end, with the first and second portions of the first sheet material being substantially adjacent to the first and second portions of the second sheet material, respectively,

folding the cut end of the first portion of said first sheet material to provide an end having a predetermined configuration,

folding the cut end of the second portion of said second sheet material to provide an end having a predetermined configuration,

joining the cut ends of the first and second portions of said first and second sheet materials, respectively, to form a first composite sheet conductor having first and second edges, corresponding to the first and second edges, respectively, of the first and second sheet materials, with the predetermined configurations of their cut and folded ends defining a notch in the second edge thereof which extends at least to the midpoint of the width of the first composite sheet conductor,

folding the cut end of the second portion of said first sheet material to provide an end having a predetermined configuration,

folding the cut end of the first portion of said second sheet material to provide an end having a predetermined configuration,

joining the cut ends of the second and first portions of said first and second sheet materials, respectively, to for a second composite sheet conductor having first and second edges, corresponding to the first and second edges, respectively, of the first and second sheet conductors, with the predetermined configurations of their cut and folded ends defining a notch in the first edge thereof which extends at least to the midpoint of said second composite sheet conductor,

directing the first composite sheet conductor through the notch in said second composite sheet conductor, and directing the second composite sheet conductor through the notch in. said first composite sheet conductor,

whereby the first and second composite conductors have different positions relative to one another, on opposite sides of the notches.

2. The method of claim 1 wherein the steps of cutting the first and second sheet materials provide cut edges which are diagonal to their first and second edges, with the slops of the diagonal cuts on the first and second sheet materials being equal in magnitude but of opposite sign, to form triangular points on their cut ends.

3. The method of claim 2 wherein the steps of folding the cut ends of the first and second portions of the first and second sheet materials fold each of their triangular points along a fold line which extends perpendicularly from the edge which joins the diagonally cut edge at the apex of the triangular point, to the diagonally cut edge.

4. The method of claim 3 wherein the dimensions of the fold lines which fold the triangular points of the first and second portions of the first and second sheet materials is less than half the width of its associated sheet material.

5. The method of claim 3 including the step of electrically joining the diagonally cut edges of the folded portions to the adjacent portions of the sheet materials, on each of the first and second portions of the first and second sheet materials.

6. The method of claim 1 including the step of providing a sheet of electrical insulating material having first and second edges, cutting the sheet of electrical insulating material to provide first and second cuts which extend inwardly from the first and second edges thereof, respectively, for a predetermined dimension, disposing the sheet of electrical insulating material between the first and second sheet of electrically conductive material, with the first sheet material proceeding through the second cut in the sheet of insulating material, and the second sheet material proceeding through the first cut, at the point of transposing the first and second electrically conductive sheet materials.

7. The method of claim 1 including the step of providing first and second sheet of electrical insulating material each having first and second edges, cutting each of the first and second sheets of electrical insulating material inwardly from one edge thereof, and interleaving the first and second sheets of electrical insulating material with the transposed first and second sheets of electrical conductive material, with the first electrically conductive sheet material and the first sheet of insulating material proceeding through the cut in the second sheet of insulating material, and with the second'electrically conductive sheet material and the second sheet of insulating material proceeding through the cut in the first sheet of insulating material.

8. The method of claim 1 including the steps of marking the first sheet material, before the cutting thereof, with first,

second and third bend lines, with the first bend line extending between the first and second edges of the sheet and having a predetermined dimension, and with the second and third bend lines starting at the intersection of the first bend line with the second and first edges, respectively, and extending outwardly from the first bend line on predetermined opposite sides thereof, intersecting the opposite edge said predetermined dimension from the intersection of the first bend line with that edge, and marking the second sheet' material, before the cutting thereof, with first, second and third bend lines which are disposed in the mirror image of the first, second and third bend lines, respectively, of said first sheet material, and wherein the steps of folding the cut ends of the first and second portions of the first and second sheet materials follow at least portions of the first, second and third bend lines.

9. The method of claim 8 wherein the steps of folding the cut ends of the first and second portions of the first and second sheet materials provide three thicknesses of sheet material where the portions are joined to form the composite sheet conductors.

10. The method of claim 8 wherein the step of folding the cut ends of the first and second portions of the first and second sheet materials provide for thicknesses of sheet material where the portions are oined to form the composite sheet conductors.

11. The method of claim 8 wherein the cutting of said first sheet material is along a line which is generated by drawing a first line through the midpoint of the first bend line, which intersects the second and third bend lines, with the slope of the first bend line being that necessary to provide a length equal to twice the desired dimension from the apex of the notch in the sheet material to the edge nearest the apex of the notch, and by drawing second and third lines perpendicular to the first and second edges, respectively, to the intersections of the first line with the third and second bend lines, and wherein the cutting of said second sheet material is along a line which is the mirror image of the cut line on the first sheet material.

12. The method of claim 8 wherein said first bend lines are perpendicular to the edges of said first and second sheet materials.

13. The method of claim 8 wherein said first bend lines deviate from a line perpendicular to the edges of the first and second sheet materials by a predetermined angle, and with the second and third bend lines being disposed to intersect those angles between the first bend lines and the first and second edges of the sheet materials which are less than 14. The method of claim 8 including the step of electrically joining the edges of at least certain .of the folded sheet materials, to the portion of the sheet material it is folded against. 

